Method and system for adjusting source impedance and maximizing output by RF generator

ABSTRACT

An electrosurgical system includes an electrosurgical probe connected to a control console, wherein the probe is capable of coagulating and ablating tissue depending on a selected operating mode. Before operating the system, probe-specific data stored in a memory device associated with the probe is read by a processing device in the console. The data includes source impedance values specific to a coagulation or cutting mode of operation. A constant duty cycle value for a modulated cutting mode also is provided. Depending on the operating mode selected, an RF generator adjusted to have a predetermined source impedance value provides a voltage value to the probe. During the duty-cycled mode, the RF generator generates an instantaneous voltage value output for a duty cycle portion that is less than 100% of a time period, which value is no less than a maximum continuous average voltage value for the electrosurgical probe.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. Ser. No. 14/156,551, filed Jan. 16, 2014,which is a divisional of U.S. Ser. No. 12/661,340, filed Mar. 16, 2010,which issued as U.S. Pat. No. 8,672,934, which claims the benefit ofU.S. Provisional Ser. No. 61/210,330, filed Mar. 17, 2009, the contentsof all of which are incorporated herein by reference.

FIELD OF THE INVENTION

This invention is related generally to an electrosurgical system havingan RF generator with a variable source impedance for providing a maximumRF power value to an RF probe, and having a cutting duty cycle valuethat provides increased instantaneous voltage to the probe for cuttingtissue.

BACKGROUND OF THE INVENTION

Endoscopy in the medical field allows internal features of the body of apatient to be viewed without the use of traditional, fully-invasivesurgery. Endoscopic imaging systems enable a user to view a surgicalsite and endoscopic cutting tools enable non-invasive surgery at thesite. For instance, an RF generator provides energy to a distal end tipof an RF probe within the surgical site. In one mode, the RF probeprovides RF energy at a power level to ablate or otherwise surgicallyremove tissue. In another instance, RF energy is provided to the RFprobe in order to coagulate the tissue at the surgical site to minimizebleeding thereat.

Tissue ablation is achieved when a high power electrical signal having asufficiently large voltage is generated by the control console anddirected to the attached probe. Application of the high power signal tothe probe results in a large voltage difference between the twoelectrodes located at the tip of the probe (presuming a bipolar probe),with the active electrode being generally 200 volts more than thepassive or return electrode. This large voltage difference leads to theformation of an ionized region between the two electrodes, establishinga high energy field at the tip of the probe. Applying the tip of theprobe to organic tissue leads to a rapid rise in the internaltemperature of the cells making up the neighboring tissue. This rapidrise in temperature nearly instantaneously causes the intracellularwater to boil and the cells to burst and vaporize, a process otherwiseknown as tissue ablation. An electrosurgical “cut” is thus made by thepath of disrupted cells that are ablated by the extremely hot, highenergy ionized region maintained at the tip of the probe. An addedbenefit of electrosurgical cuts is that they cause relatively littlebleeding, which is the result of dissipation of heat to the tissue atthe margins of the cut that produces a zone of coagulation along the cutedge.

In contrast to tissue ablation, the application of a low powerelectrical signal having a relatively low voltage to the activeelectrode located at the tip of the probe results in coagulation.Specifically, the lower voltage difference established between theactive and return electrodes results in a relatively slow heating of thecells, which in turn causes desiccation or dehydration of the tissuewithout causing the cells to burst.

Basic operation of an electrosurgical system can be analyzed in view ofat least two relationships.

The first relationship is described by Ohm's law, which in simplestterms, is represented by the equation V=I×R or alternatively V=(I×Z),where:

I=electrical current;

R=resistance or impedance to the current (hereafter referred to asImpedance (Z), which includes capacitive and inductive loading); and

V=voltage or force that “pushes” the current through the impedance.

The second relationship is the definition of power (P), which can becalculated by the equation (P=I×V). The resultant product of current Iand voltage V represents the amount of energy that is transferred withina defined period of time.

FIGS. 1 and 2 correspond to FIGS. 1 and 2 of U.S. Patent Publication2007/0167941, the disclosure of which is hereby incorporated byreference.

As illustrated in FIG. 1, a typical electrosurgical system 10 includesan electrosurgical probe 12 (hereafter referred to simply as “probe”)and a control console or controller 14. The probe 12 generally comprisesan elongated shaft 16 with a handle 18 at one end and a tip 20 at theopposite end. A single active electrode 19 is provided at the tip 20 ifthe probe 12 is of a “monopolar” design. Conversely, the probe 12 may beprovided with both an active electrode 19 and a return electrode 21 atthe tip 20 if the probe is “bipolar” in design. The probe 12 connects tocontrol console 14 by means of a detachable cable 22. The current forenergizing the probe 12 comes from control console 14. When actuated,the control console 14 generates a power signal suitable for applyingacross the electrode(s) located at the tip 20 of the probe 12.Specifically, current generated by the control console 14 travelsthrough the cable 22 and down the shaft 16 to tip 20, where the currentsubsequently energizes the active electrode 19. If the probe 12 ismonopolar, the current will depart from tip 20 and travel through thepatient's body to a remote return electrode, such as a grounding pad. Ifthe probe 12 is bipolar, the current will primarily pass from the activeelectrode 19 located at tip 20 to the return electrode 21, also locatedat tip 20, and subsequently along a return path back up the shaft 16 andthrough the detachable cable 22 to the control console 14.

Configuration of the control console 14 is carried out by means of aninterface 15, while actuation and control of the probe 12 by the surgeonis accomplished by one or more switches 23, typically located on theprobe 12. One or more remote controllers, such as, for example, afootswitch 24 having additional switches 26 and 28, respectively, mayalso be utilized to provide the surgeon with greater control over thesystem 10. In response to the surgeon's manipulation of the variousswitches on the probe 12 and/or remote footswitch 24, the controlconsole 14 generates and applies either a low power signal or high powersignal to probe 12. As will be discussed in greater detail below,application of a low power signal to probe 12 results in coagulation ofthe tissue adjacent the tip 20 of the probe 12. In contrast, applicationof a high energy signal to probe 12 results in tissue ablation.

While operating in coagulation mode, the control console 14 of the priorart system shown in FIG. 1 is configured to drive the attached probe ata low, but constant, power level. Due to inherent varying conditions intissue (i.e., the presence of connective tissue verses fatty tissue, aswell as the presence or absence of saline solution), the impedance orload that the system experiences may vary. According to Ohm's law, achange in impedance will result in a change in current levels and/or achange in voltage levels, which in turn, will result in changing powerlevels. If the operating power level of the system changes by more thana predefined amount, the control console will attempt to compensate andreturn the power back to its originally designated level by regulatingeither the voltage and/or current of the power signal being generated bythe console and used to drive the attached probe.

While operating in tissue ablation mode, the control console of thesystem shown in FIG. 1 is configured to drive the attached probe at ashigh a power level as possible without exceeding a maximum average powerlevel, which in some instances may equal 400 watts.

The electrosurgical system shown in FIG. 1 modulates the entire powersupply signal as a whole, turning the signal on and off in a mannersimilar to a pulse width modulated (PWM) signal. Furthermore, the powersignal is dynamically modulated on and off so as to behave like a PWMsignal having a variable duty cycle. As a result, the percentage of timethat the power signal is “on”, compared to the percentage of time thatthe signal is “off”, will vary depending on the percentage of time thatthe power levels of the signal exceed the maximum limit over apredetermined interval of time.

Consequently, the duty cycle of the power signal is dynamicallymodulated so that even though the power levels of the signal may brieflyexceed the maximum power limit for a portion of time during a specifiedinterval, the average power level over that interval of time remainsacceptable.

To further illustrate the above point, FIG. 2 depicts several examplesof high frequency power signals generated by the control console 14 overa 20 millisecond period of time and used to drive the attached probe 12.Signal A is a power signal in the form of a 200 KHz sine wave. Nomodulation of signal A is present with respect to a signal duty cycle,resulting in a power signal that is continuously on (i.e., 100% dutycycle) for the entire 20 millisecond duration.

In FIG. 2, signal B is similar to signal A, but has been brieflymodulated roughly half-way through the 20 millisecond period. In thisinstance, for example, changing environmental variables may haveresulted in the power level of the signal briefly exceeding anestablished maximum limit during the previous 20 millisecond period (notshown). To compensate for this prior spike in power level and assurethat the average power of the signal does not exceed a maximum limit,the system briefly modulates signal B during the next 20 millisecondperiod (shown), effectively turning the signal off for a moment. Thus,for example, signal B is modulated or turned off for approximately 5milliseconds during the 20 millisecond period depicted, resulting in thesignal effectively having a 75% duty cycle for the period shown.

To compensate for power level spikes that are larger in magnitude orlonger in duration, the system dynamically modulates the duty cycle ofthe power signal during the next monitoring interval to effectively turnoff the signal for a longer period of time. For example, signal C ofFIG. 2 is similar to signal B, but is modulated to have a lower dutycycle, resulting in signal C being turned off for a longer period oftime during the 20 millisecond interval shown.

By dynamically adjusting a duty cycle of the power signal, the averagepower of the signal can be maintained below an established maximum powerlimit. Furthermore, it has been observed that the ionized high energyfield maintained at the tip of the probe 12 does not collapse, butremains stable, if the effective duty cycle of the power signal ismodulated quickly enough (i.e., turning the signal on or off inincrements of 50 milliseconds over a 1 second period).

In the electrosurgical system 10 illustrated in FIG. 1 above, the dutycycle is varied for the waveform only in instances where the voltage orcurrent causes the power value of the RF probe to exceed the acceptablepower value. Thus, in the prior art, the duty cycle is varied bydiffering amounts, as necessary, to account for unintended increases inpower value beyond the average power value of the system.

A non-volatile memory device (not shown) and reader/writer (not shown)can be incorporated into the body 18 of the probe 12, or alternatively,incorporated into or on the cable 22 that is part of the attachableprobe and which is used to connect the probe 12 to the control console14 of the system. Alternatively, the memory device may be configured soas to be incorporated into or on the communication port that is locatedat the free end of the cable 22 and which is used to interface the cablewith a corresponding port on the controller 14.

During manufacturing of the attachable probe shown in FIG. 1, datarepresenting probe-specific operating parameters is loaded into thememory device. Upon connection of the attachable probe 12 to the controlconsole 14 of the system 10, the data stored in the probe's non-volatilememory can be accessed by the reader and forwarded on to the controller14. As such, once a probe 12 is connected, the controller 14 accessesthe configuration data of the specific probe 12 and automaticallyconfigures itself based on the operating parameters of the probe 12.

Beyond probe-specific operating parameters, the prior art memory devicewithin each attachable probe 12 can store additional data concerningusage of the probe 12. This usage data can comprise a variety ofinformation. For example, usage data may represent the number of times aprobe 12 has been used, or the duration of the time that the probe hasbeen activated overall or at different power levels. Additional usagedata may restrict the amount of time that a specific attachable probecan be used. Alternatively, a probe 12 may be programmed so it can onlybe used for a limited duration of time starting from the moment theprobe was first attached to a control console and powered up. Forexample, a probe may be programmed to that it only functions for a24-hour period starting from when the probe is first activated. Based ona clock maintained within the control console, a time stamp is writtento the memory device of the probe when the probe is attached to theconsole for the first time and powered up. Any later attempted use ofthat probe will trigger a comparison of the stored time stamp to thecurrent time reported by the control console, and if the allotted amountof time has already passed, the system will not allow the probe to beused.

Alternatively, a specific prior art probe is dynamically restricted, sothat the overall amount of time allocated for use of the probe will varydepending not only on the amount of time the probe has been used, butalso the power levels that the probe was driven at during its use. Assuch, a specific attachable probe may be limited to 1 hour of use ifalways driven at a maximum power, but may be usable for 3 hours if allprior uses occurred at substantially lower power levels.

In addition to usage data, the prior art memory device can storeinformation concerning any errors that were encountered during use ofthe probe 12. For example, the failure of a probe to activate would leadthe control console 14 to issue and store one or more error codes intothe probe memory. Technicians can later retrieve these error codes toaid in their examination of the failure.

In addition to probe-specific operating parameters and usage data, thememory device incorporated into each probe may also be programmed by themanufacturer to include software scripts or updates for the controlconsole of the system.

In the electrosurgical system illustrated in FIG. 1, the power outputfrom control console 14 has a constant source impedance regardless ofthe probe utilized or the mode of operation.

As discussed above, the electrosurgical system 10 shown in FIG. 1provides a modulated duty cycle power output only to decrease poweroutput in instances where the power exceeds the desired power due toincidental variations in the impedance of the load or other powercontrol issues. Further, the duty cycle value varies depending on theamount that the power exceeds the desired average power level. Thus,during normal operation, the output power value may, in some instances,not exceed the desired intended constant average power value resultingin no duty cycle variations in the power output by an energy generator.

The present invention is directed to improving cutting or coagulation oftissue by an RF probe, such as by optimizing power delivery to tissue byadjusting the source impedance value of an RF generator.

In one embodiment of the invention, information regarding sourceimpedance values for an RF generator is stored on an RF probe and readby a processing device. The processing device controls the sourceimpedance value of the RF generator based on the stored values tooptimize power transfer from the RF generator to tissue via the RFprobe.

In another embodiment of the invention, improved operation of anelectrosurgical system is obtained by duty cycling of voltage outputfrom a RF generator to increase the instantaneous voltage value appliedto an RF probe. The duty cycling information is read from a memorydevice on the RF probe. Modulating the RF voltage value at a secondaryfrequency with a duty cycle of less than 100% reinitiates a voltage arcdynamically on different tissues at the beginning of each time periodthat includes the duty cycle value. Periodically reinitiating arcing byduty cycling the RF output voltage value helps to maintain consistentburn characteristics on various tissues. Also, constant duty cyclingtends to physically push tissue away from the probe tip during ablationto maintain good spacing between the probe tip and tissue, which createsoptimal arcing, and thus helps to prevent clogging. Further, the dutycycling of output voltage helps to control depth of necrosis because theheated tissue is allowed to thermally relax between each duty cycleapplication of RF voltage.

Another advantage of the invention is that the duty cycle applied to theRF voltage output decreases the amount of total time the probe isexposed to high RF voltage, which reduces probe degradation as comparedto a continuous application of RF power. In this embodiment, cyclicallyapplying voltage to the RF probe at less than the maximum allowablevoltage value, or even at the same voltage value as a non-duty cycled RFgenerator output, reduces heating of the surgical site, such as a joint,without significantly affecting cutting performance.

One aspect of the invention is directed to a method of controllingsource impedance of an RF generator in a control console for anelectrosurgical system including an electrosurgical RF probe, thecontrol console being in communication with a memory device associatedwith the RF probe, the method including the steps of: connecting theelectrosurgical RF probe to the control console having the RF generator,the memory device associated with the RF probe providing probe-specificdata stored in the memory device to a processing device in the controlconsole, the probe data including at least a first source impedancevalue corresponding to a coagulation operating mode for the RF probe anda second source impedance value corresponding to a cutting operatingmode for the RF probe; selecting the coagulation operating mode or thecutting operating mode, the processing device operating so that thesource impedance of the RF generator has a source impedance valuecorresponding to the first source impedance value when the coagulationoperating mode is selected by an operator and so that the sourceimpedance of the RF generator has the second source impedance value whenthe cutting operating mode is selected by an operator; and operating theRF probe to coagulate or cut tissue at a surgical site.

A further aspect of the invention is directed to a method of controllinga cutting operation for an electrosurgical cutting system including acontrol console, an RF generator, and an electrosurgical RF probe, themethod including the steps of: connecting the RF probe associated with amemory device to the control console to provide probe-specific datastored in the memory device to a processing device in the controlconsole, the probe data comprising a maximum continuous average voltagevalue and a constant duty cycle value of less than 100% andcorresponding proportionally to a time period defined by a secondaryfrequency value, the processing device having a maximum instantaneousvoltage value based on the probe data; and actuating the RF generator tooutput an instantaneous voltage value in a range that is not less thanapproximately the maximum average voltage value and that is not greaterthan approximately the maximum instantaneous voltage value to the RFprobe to cut tissue during the constant duty cycle value which includesa first portion of the time period, and wherein no voltage value isoutput by the RF generator or applied to the RF probe during a secondremaining portion of each time period.

A still further aspect of the invention is directed to a method ofcontrolling the operation of an RF generator disposed in a controlconsole of an electrosurgical system including an electrosurgical RFprobe having a memory device, the method including the steps of:connecting the electrosurgical RF probe having the memory device to thecontrol console, a processing device disposed in the control console forreceiving probe-specific data stored in the memory device, theprobe-specific data comprising a constant continuous coagulation voltagevalue, maximum continuous average voltage value and a constant cuttingduty cycle value for operating the probe in a cutting operating mode,the processing device provided with a maximum instantaneous voltagevalue related to the maximum continuous average voltage value and aconstant duty cycle value; selecting a coagulation operating mode or thecutting operating mode, wherein in the cutting operating mode theoperator selects a continuous cutting mode or a modulated cutting mode,wherein in the modulated cutting mode the RF generator intermittentlyoutputs to the RF probe an instantaneous voltage value that is no lessthan the maximum continuous average voltage value and no more than themaximum instantaneous voltage value, the constant cutting duty cyclevalue being defined as a percent value that is less than 100%, andwherein the instantaneous voltage value is applied to the probe duringthe constant cutting duty cycle value of a time period that is definedby the inverse of a first secondary frequency value, the intermittentapplication of the instantaneous voltage value enabling cutting oftissue, and wherein in the coagulation operating mode the RF generatoroutputs the constant continuous coagulation voltage value for obtaininga desired coagulation effect; and operating the electrosurgical systemto coagulate or cut tissue at a surgical site.

A further aspect of the invention is directed to an electrosurgicalsystem, including: a control console having a processing device disposedtherein; an electrosurgical probe that detachably connects to thecontrol console; an RF generator for generating a voltage value forenergizing the electrosurgical probe; and a memory device associatedwith the RF probe, the memory device storing probe-specific operatingparameters including a cutting duty cycle value for a cutting mode,wherein the processing device obtains the probe-specific parameters fromthe memory device and after selection of the cutting mode, theprocessing device controls the RF generator to output an instantaneousvoltage value for the constant cutting duty cycle portion of each timeperiod defined by the inverse of a secondary frequency, wherein theinstantaneous voltage value is intentionally greater than a maximumaverage voltage value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an electrosurgical system that includes anelectrosurgical probe connected to a control console, along with afootswitch.

FIG. 2 depicts examples of high frequency RF signals generated by thecontrol console shown in FIG. 1 for driving the attached probe.

FIG. 3 depicts an electrosurgical system of the invention that includesa footswitch, an electrosurgical probe and a powered surgical handpiecefor attachment to a control console.

FIG. 4 is a block diagram illustrating components of the control consoleand the powered handpiece of FIG. 3.

FIG. 5 illustrates a graph showing delivered power versus load impedancefor a number of different source impedances of an RF generator.

FIG. 6 is a flowchart showing steps for configuring of an RF generatorwith a predetermined source impedance value depending on selectedoperating modes.

FIG. 7 is a graph illustrating a normal RF waveform and a duty cycled RFwaveform.

FIG. 8 is a flowchart showing selection of a continuous operation orduty cycled operation of an RF generator after selection of acoagulation or cutting mode.

DETAILED DESCRIPTION

FIG. 3 shows a surgical system 30 including a console 32 having afootswitch receiving port 34, a handpiece receiving port 36 and a RFprobe receiving port 38. The footswitch receiving port 34 provides aconnection to the control console 32 for a footswitch 40. Handpiecereceiving port 36 receives the connection jack of a powered surgicalhandpiece 42 with a cutting element or burr 43 attached thereto. Oneconventional handpiece is disclosed in U.S. Patent Publication No.2003/0093103, the disclosure of which is hereby incorporated byreference herein. RF probe receiving port 38 receives a connecting jackof an RF probe 44.

As shown in FIG. 4, the powered handpiece 42 of the surgical system 30includes an antenna 46. In one embodiment, a non-volatile memory device,such as an RFID chip 48, is provided in the cutting element 43. Atransceiver 47 located in the control console 32 is connected to theantenna 46 for reading probe-specific data. Antenna 46 carries powerfrom the transceiver 47 to the RFID chip 48 in the cutter element 43 andreturns data from the chip to the transceiver. In some embodiments, thetransceiver 47 also writes data to the RFID chip 48.

One embodiment of the RF probe 44 generally corresponds to the probestructure illustrated in FIG. 1, except additional probe-specific data,described later herein, is provided on a one-wire memory device andprovided to the control console 32. The console 32 includes a processingdevice 50 for processing the data received from the one-wire memorydevice. The processing device 50 controls an RF generator 52 thatprovides RF energy to the RF probe 44 to power an electrode 54 at thedistal end thereof. In one embodiment, the RF probe 44 and the electrode54 form a disposable unit.

The embodiments of FIGS. 3 and 4 include the powered handpiece receivingport 36 that enables the control console 32 to provide power to surgicalhandpiece 42. The surgical handpiece 42 enables mechanical cutting anddebridement of bone and soft tissue.

RF Generator Source Impedance

FIG. 5 shows a graph plotting power delivered (watts) versus loadimpedance Z_(L) (ohms) for a single electrosurgical probe. The graphshows power delivered values versus load impedance values for fivedifferent RF generator source impedances Z_(source) as represented byrespective plotted lines on the graph. The source impedance valuesZ_(source) are 200Ω, 225Ω, 250Ω, 275Ω and 300Ω.

In general, when the load impedance is low, the power delivered is lowto prevent a large current from passing through the electrode 54. Such alarge current may cause electric shock or other dangerous conditions andthus is prevented by current limiting circuitry in the RF generator 52.

Different RF probes 44, due to their shape, size or other factors,result in different load impedances Z_(L) provided to the console forthe same tissue type or tissue characteristics. Thus the RF generator 52may provide optimal delivered power for the RF probes, as shown in FIG.5, by adjusting the source impedance.

The load impedance value Z_(L) is also affected greatly by whether thetissue is being cut or the tissue is being coagulated. Further, thetemperature of the joint being operated on and the amount of fluid inthe joint also can affect the load impedance value Z_(L).

Since various RF probes 44 are intended for use in various surgicaloperations, the load impedance range of use for cutting is predictable.Thus, the source impedance value Z_(source) that provides the highestdelivered power in the expected load impedance range is stored in theRFID memory chip 48 and is provided to the processing device 50.Therefore, different source impedance values Z_(source) are provided forvarious different RF probes 44 depending on the probe structure and theintended use of the probe.

In some embodiments, the RFID chip 48 includes one or more values forthe source impedance of the RF generator 52 for use with the particularprobe. For instance, one source impedance value, such as 200Ω, may beprovided for a coagulation operation and another source impedance value,such as 250Ω, may be provided for the RF generator 52 when the RF probe44 is utilized for cutting tissue or ablation.

Operation of one embodiment of a surgical system 30 having dynamicsource impedance values Z_(source) is illustrated in FIG. 6. At step 60,the jack or connector of the RF probe 44 is inserted into thecorresponding probe receiving port 38 on the control console 32. Then,at step 62, the processing device 50 of the console 32 automaticallyreceives the probe data stored in the RFID chip 48. The probe dataincludes RF generator source impedance values Z_(source) for differentoperating conditions of the specific RF probe 44. At step 64, the userthen selects either a cutting mode or a coagulation mode. If acoagulation mode is selected, the processing device 50 advances to step66. At step 66, the processing device 50 operates on circuitry withinthe control console 32 to provide a stored coagulation source impedancevalue Z_(source) to the RF generator 52 for the coagulation mode. Then,at step 70, the processing device 50 returns to a control mode whereinthe RF generator 52 is selectively controlled by a user to apply RFenergy and coagulate tissue or veins.

If the cutting mode is selected at decision step 64, the processingdevice 50 advances to step 68. At step 68, the processing device 50controls circuitry so that the RF generator 52 is provided with acutting source impedance value Z_(source) that was previously read bythe processing device 50 from the RFID chip 48. Therefore, asillustrated in FIG. 6, in operation, the RF generator 52 is providedwith a source impedance value Z_(source) that maximizes the powerdelivered during operation of the RF probe 44 in either operating mode.

Increasing Instantaneous Power

As discussed above, in many surgical devices the maximum amount of powermandated for use with a probe is 400 watts per second. Some embodimentsof the invention provide a greater instantaneous power to tissue whilemaintaining the overall specified average power of, for example, 400watts/second. Some embodiments provide RF power to the probe 44 at aspecified predetermined constant duty cycle of a time period T definedby a secondary frequency value f that is less than the RF frequency.Specifically, time period T is the inverse of the frequency f and thusequals 1/f. Therefore, instantaneous power delivered can be increasedwithout exceeding a maximum total power requirement for a given timeperiod.

This approach for increasing the instantaneous power is described by theequation set forth below.P _(inst) =P _(ave)÷duty cycle %

In the above equation, P_(ave) is an average constant continuous powervalue that provides maximum allowable power to an electrosurgical probe,such as 400 watts per second. P_(inst) is a maximum instantaneous powervalue greater than the constant continuous average power P_(ave).P_(inst) is determined by P_(ave) and a duty cycle percent value. Thesmaller the duty cycle value, the greater the value for P_(inst).

In FIG. 7, a normal RF waveform has a constant voltage value Vnom, whichat a constant load impedance value Z_(L) provides a constant averagepower value P_(ave). Thus, after the beginning start-up of voltageapplied to the RF probe 44, nominal voltage V_(nom) is appliedcontinuously, to obtain the constant average power value P_(ave) for theentirety of the illustrated normal RF waveform.

An improvement in power applied to an RF probe 44, at least undercertain conditions, is illustrated by the duty cycled RF waveform alsoshown in FIG. 7. As discussed above, the duty cycled waveform has a timeperiod T that is defined by the inverse of the secondary frequency valuef. As discussed above, the secondary frequency value f must be much lessthan the RF frequency value applied to the RF probe 44. The secondaryfrequency value, in some embodiments, has a value of 20 Hz.

The over voltage value V_(ov) shown in FIG. 7 at a constant loadimpedance value Z_(L) provides the instantaneous maximum power valueP_(inst) described above. The over voltage value V_(ov) is greater thanthe voltage value V_(nom) as a result of the off portion t_(off) of eachtime period T. Thus, voltage value V_(ov) shown in FIG. 7 and applied toRF probe 44 by the RF generator 52 results in an instantaneous powervalue P_(inst) that is greater than a corresponding average power valueP_(ave) even though total power over time periods T is about the same.

In FIG. 7, the duty cycle t_(on) is approximately 75% of the period Tand the off portion t_(off) is approximately 25% of the time period T.If the constant duty cycle were decreased from 75% to 50% in anotherembodiment, the over voltage value V_(ov) applied for each duty cyclewould then increase resulting in an increase in the instantaneous powervalue P_(inst) as set forth in the above power equation. Again, theembodiment illustrated in FIG. 7 is plotted with the load impedancevalue Z_(L) having a constant value for the entirety of the timeillustrated along the length of the x-axis.

If there are changes in load impedance Z_(L) along the time axis shownin FIG. 7 for the duty cycled RF waveform, the overvoltage value V_(ov)generally is maintained and thus the instantaneous power value P_(inst)for the duty cycle t_(on) of each time period T may vary slightly. Thusthe Z_(source) value must be as close as possible to Z_(Load) tomaximize power output from the RF probe 44.

As in the source impedance embodiment discussed above, maximum power andduty cycle control information can be stored in the memory device, alongwith other RF probe data, as well as source impedance values Z_(source).

Operation of the RF probe 44 in the instantaneous increased powerarrangement having a duty cycled RF waveform is explained in the flowchart of FIG. 8. In step 78 of FIG. 8, the RF probe 44 is plugged intothe RF probe receiving port 38. At step 80, probe-specific data is readfrom the memory device by the processing device 50. In some embodiments,probe data read by the processing device 50 disposed in the console 32includes probe-specific duty cycle values for both coagulation modes andcut modes. In some embodiments, a secondary frequency value is alsoprovided. In some embodiments, a probe-specific constant voltage valuefor a continuous coagulation mode can be provided.

At decision step 82, the user selects either the coagulation mode or thecutting mode. If the cutting mode is selected, the processing device 50advances to decision step 84. At decision step 84, a user selectsbetween cutting with a duty cycle or operating at a continuous voltagecut value. If the user selects operation at a continuous voltage value,the processor 50 advances to step 86 and in view of the probe datacontrols the RF generator 52 to output the non-duty cycle maximumaverage voltage V_(nom). Then, at step 88, the processing device 50returns to enable powering of the RF generator 52 by a user at thecontinuous voltage cut value, corresponding to the maximum average powervalue P_(ave).

If the operator decides to cut tissue with a duty cycle arrangement atstep 84, the processing device 50 advances to step 90. At step 90, theprocessor device 50 calculates instantaneous power value P_(inst) fromthe stored duty cycle percentage value read from the memory device andthe average power value P_(ave). The processor device 50 then calculatesan expected over voltage value V_(ov) that is intended to result in theinstantaneous power value P_(inst) during the duty cycle. The processingdevice 50 then advances to step 92 and returns to enable operation inthe duty cycled cutting mode.

Returning to step 82, if the operator selects the coagulation mode, theprocessing device 50 advances to decision step 94. At decision step 94,if the user selects operating the RF probe 44 at a continuouscoagulation power value, the processor device 50 advances to step 96 andconfigures or controls the RF generator 52 for operation at anessentially constant continuous voltage value that coagulates tissue andthen returns at step 88 to permit operation of the RF probe 44.

At decision step 94, if the user decides to perform coagulation with aduty cycled value, the processing device 50 advances to step 98. At step98, a coagulation duty cycle power value is obtained by dividing theaverage desired coagulation power value by a duty cycle value receivedby the processing device 50 from the memory device. The instantaneouspower value is then converted to a coagulation operating voltage andoutput by the RF generator 52 for the duty cycle t_(on) of the timeperiod T.

As with the above embodiments directed to RF generator source impedancevalues Z_(source) discussed above, in these additional embodiments thesecondary frequency value f, and especially the stored duty cycle valuesmay vary for different types of probes and may also vary for thecoagulation mode and the cutting mode for any given RF probe. In otherembodiments, the secondary frequency value f is a constant value for allRF probes and is stored in the processing device 50.

While FIG. 8 shows manual selection of a continuous essentially constantvoltage value or of a duty cycled voltage value provided to an RF probe44, in another embodiment a duty cycled power value is output from theRF probe automatically in the coagulation mode. In other embodiments, acontinuous constant voltage is output by the RF generator in everyinstance that the coagulation mode is selected.

While FIG. 8 does not show the selection of a source impedance value,the value Z_(source) can be provided to control the RF generator 52along with the stored duty cycle value at step 90 or at step 98.

While the disposable RF probe 44 is disclosed as having a one-wirememory device or an RFID chip, other non-volatile memory devices arealso contemplated.

In another embodiment of the invention, the normal nominal voltage valueV_(nom) illustrated in FIG. 7 for a continuous mode, operates as an RFgenerator 52 output voltage value V_(nom) during on periods t_(on) of aduty cycle. This embodiment has an improved cooling effect on the tissueand arc reinitiation provides a desired cutting effect despite a lesseramount of voltage being applied to the tissue over time period T.

In another embodiment of the invention, a voltage value between V_(nom)and V_(ov) having a duty cycle is applied to the RF probe 44. Thisvoltage value, determined by the processor device 50, maximizesperformance by providing cooling during time t_(off) while providing avoltage value greater than or equal to V_(nom) during t_(on).

In another embodiment of the invention, a blend mode providingsimultaneous cutting and coagulation of tissue may be provided by the RFgenerator 52. In this arrangement, a specific source impedance valuethat is different from the source impedance value for other modes iscontemplated.

In some embodiments, the RF probe 44 has a bipolar electrode and inother embodiments the RF probe has a monopolar electrode.

In some embodiments, the handpiece structure of the RF probe 44 is notdisposable. In these embodiments the electrode 54 projecting from thedistal end of the probe body is detachably coupled to the probe body.

Although particular preferred embodiments of the invention are disclosedin detail for illustrative purposes, it will be recognized thatvariations or modifications of the disclosed apparatus, including therearrangements of parts, lie within the scope of the present invention.

What is claimed is:
 1. Method of controlling the operation of an RFgenerator disposed in a control console of an electrosurgical systemincluding an electrosurgical RF probe having a memory device, the methodcomprising the steps of: connecting the electrosurgical RF probe havingthe memory device to the control console, a processing device disposedin the control console for receiving probe-specific data stored in thememory device, the probe-specific data comprising a constant continuouscoagulation voltage value, maximum continuous average voltage value anda constant cutting duty cycle value for operating the probe in a cuttingoperating mode, the processing device provided with a maximuminstantaneous voltage value related to the maximum continuous averagevoltage value and a constant duty cycle value; selecting a coagulationoperating mode or the cutting operating mode, wherein in the cuttingoperating mode the operator selects a continuous cutting mode or amodulated cutting mode, wherein in the modulated cutting mode the RFgenerator intermittently outputs to the RF probe an instantaneousvoltage value that is no less than the maximum continuous averagevoltage value and no more than the maximum instantaneous voltage value,the constant cutting duty cycle value being defined as a percent valuethat is less than 100%, and wherein the instantaneous voltage value isapplied to the probe during the constant cutting duty cycle value of atime period that is defined by the inverse of a first secondaryfrequency value, the intermittent application of the instantaneousvoltage value enabling cutting of tissue, and wherein in the coagulationoperating mode the RF generator outputs the constant continuouscoagulation voltage value for obtaining a desired coagulation effect;and operating the electrosurgical system to coagulate or cut tissue at asurgical site.
 2. The method of claim 1, wherein the probe specific datafurther comprises a constant coagulation duty cycle value for a perioddefined by the inverse of a second secondary frequency value, that isprovided to the processing device for operating the RF generator in amodulated coagulation mode.
 3. The method of claim 2, wherein connectingthe RF probe to the control console comprises connecting a cable of theRF probe to a single RF cable port on the control console to supplypower to the RF probe.
 4. The method of claim 2, wherein the firstsecondary frequency value and the second secondary frequency value areequal and are stored in the processing device, and wherein the cuttingduty cycle value is different than the coagulation duty cycle value. 5.The method of claim 1, wherein the probe-specific data further comprisesthe maximum instantaneous voltage value, a coagulation source impedancevalue for the RF generator in the coagulation operating mode and theprobe-specific data further comprises a cutting source impedance valuefor the RF generator in the cutting operating mode.
 6. The method ofclaim 5, wherein the step of selecting the coagulation operating mode orthe cutting operating mode comprises providing the RF generator with thecoagulation source impedance value from the processing device in thecontrol console when the coagulation operating mode is selected by anoperator, and providing the RF generator with the cutting sourceimpedance value from the processing device in the control console whenthe cutting operating mode is selected by an operator, the coagulationsource impedance value being different than the cutting source impedancevalue.